Means for changing the intensity of signals in radiodynamic receiving systems



Aug. 10 1926. 1,595,177

J. H. HAMMOND. JR MEANS FOR CHANGING THE INTENSITY 0F SIGNALS IN RADIODYNAMIC RECEIVING SYSTEMS Original Filed May 6, 1918 2 Sheets-Sheet 1 M $1 2. U "4 I\ Q E v H07 car rm=------- a, won: t 8/ Iv f r VOL rs 01v 6 910.

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UNITED STATES EATENT OFFICE.

JOHN HAYS HAMMOND, 51%,, OF GLOUCESTER, MASSACHUSETTS.

MEANS FOR CHANGING THE INTENSITY OF SIGNALS IN BADIODYNAMIC RECEIVING SYSTEMS.

Application filed May 6, 1918, Serial No, 232,705. Renewed may 31, 1924.

This invention relates to means for reducing the intensity of strong signals produced through or pertaining to radiantenergy, and in certain of its aspects is an imprm'ement upon the invention disclosed in the joint application of myself and Emory Leon Chaiiee, Serial No. 177,202, filed June 27, 1917.

in order that the principle of the invention may be readily understood, I have disclosed a single embodiment thereof and the mode best known to me for practicing the same.

In the draWings,-

Fig. 1 diagrammatically representsa receiving system having my invention applied thereto;

Fig. 2 diagrammatically represents a characteristic audion curve;

Fig. 3 diagrammatically indicates certain potential rises on the grid of the electron relay;

Fig. 4 is a diagran'imatic representation of certain impulses obtained in the practice of my invention;

Figs. 5 and 6 diagrammatically indicate \ving current fluctuations in the practice of my invention; and

7 represents curves characteristic of the practice of my invention.

In accordance with my invention I provide means furnishing a leak, generally analogous to a resistance, but which is much more effective for strong signals than for weak ones, and thereby prevent the action of static or atmospheric disturbances or strong interference upon the receiving systenl.

' Referring more particularly to the drawings, I have in Fig. 1 represented the primary winding of a transformer at 1, this Winding being included in an open aerial receiving circuit comprising an antenna 2 and ground 3. The secondary Winding of the transformer is included in a closed oscillatory circuit and is indicated at 4, a tuning condenser being designated by 5, and a stoppage condenser by 6. The said stoppage condenser is in series With the grid 7 or potential gradient changing means of an audion detector, or thermionic valve, the evacuated tube whereof is indicated at 8, the plate at 9, and the heated filament or ionizing means 10, a battery 11 being grid 7 plate 9 and filament 10 are frequently termed electrodes. Leading from the secondary Winding t are conductors 12 and 13, the former of Which leads to the grid 7 and has interposed therein the said stoppage condenser 6. The conductor 13 leads to the heated filament 10.

Shunted about the stoppage condenser 6 what may be termed a variable or differential resistance or leak, which, considered as a by-pass, is much more effective for strong signals than for Weak signals. This variable or differential resistance, leak or valve, as it may be termed, is generally similar to the disclosure in the said copending application of myself and Emory Leon Chafiee, and herein comprises an evacuated tube 14: having sealed therein a plate 15, a grid 16, and a heated filament 17, a heating battery 18 being provided for the latter. The plate 15 is connected to the conductor 12 by a conductor 19, and

the heated filament 17 is connected to said conductor 12 by a conductor 20, the potentiometer 20 being preferably provided as diagrammatically indicated for fine adjust ment of the functioning voltage of the apparatus. The conductors 1.9 and 20 are at the opposite sides A, B respectively of the said stoppage condenser 6.

The action of the said variable or differential resistance or leak need not be particularly described, since generally it is the same as that disclosed in the said copending application.

The said variable or differential resistance or leak provides a by-pass which allows the stoppage condenser 6 to discharge ac cording to the potential strain produced across the plate 15 and the heated filament 17. The action of such variable or differential resistance or by-pass is to allow the charges of high potential produced in the stoppage condenser 6 by atmospheric disturbances to leak through said by-pass so that the positive charges travel from the plate 15 to the heated. filament 17 and to the side B of the condenser 6, While the negative charges travel from the side B of the condenser 6 through the filament 17 .to the plate 15, and thence to the side A of the condenser 6. This equalizes the'sign of the charges on e ther condenser plate 013 tie said stoppage condenser 6 in such a way as to reduce tl potential strain across said condenser.

The described effect occurs only when the voltage across the by-pass is of such value as to allow a discharge to take place through it. In order to facilitate such discharge, a positive potential is applied to the grid 16 by means of a battery 20 so as to steepen the potential gradient and thereby conduce to a greater emission of negative electrons from the filament 17.

In Fig. 2 I have diagrammatically repre- Sented at 21 a characteristic curve of the audion having the grid 16. The abscisia represents the voltage applied to the grid 16, as indicatec at 22, and the ordinate repre sents the value of the current flowing from the plate 15 to the heated filament 17, as indicated at 23. This curve is fairly representative of the class of three-electrode electron detectors that are fairly highly vacuized.

Extending from the plate 9 of the audion tube 8 is a conductor 24, and extending from the heated filament 10 of such audion tube is a conductor 25 having therein a battery 26. The said battery 26 is connected with the electron detector so as to produce the so called flux current or plate current.

Operatively associated with the said conductors 24 and 25 is a tuned circuit containing a condenser 27 and an induction coil 28. The circuit containing the said condenser 27 and induction coil 28 is preferably tuned to an inaudible group frequency, for example, twenty thousand cycles per second. The inductance coil 28 is inductively coupled to an inductance coil 29 which is shunted by a condenser 30. Leading from the said inductance coil 29 are conductors 31 and 32. In the case assumed, the circuit containing the inductance coil 29 and condenser 30 is likewise tuned to twenty thousand impulses per second.

If high frequency oscillations be emitted from the transmitter in groups of twenty thousand per second, and if the stoppage condenser 6 connected to the grid 7 be not short-circuited by the action of the said variable resistance or by-pass, there are obtained through the action of the audion tube 8 which constitutes an electron relay, impulses of the character indicated at 33, 33 in Fig. 4:. These impulses are rectified on account of the functioning of the electron relay 8 which has well known rectifying qualities.

On account of the storing of the charge in the stoppage condenser 6, the individual high frequency oscillations will tend to add up on the grid 16 of the audion tube 1%, thereby reducing the flux current or plate current through the said electron relay 8.

The rises of potential on the grid 16 will occur as indicated at 83 in Fig. 4, and will have a slight superimposition of the individual high frequency oscillations. The effect, however, will be to produce through the inductance coil 28 unidirectional pulses of current at the rate of twenty thousand per second, since the condenser 27 and the inductance coil 28 are in tune to this period. By means of resonance, strong oscillations will be produced in the circuit which will be transmitted by induction to the circuit containing the inductance coil 29 and the condenser 30. This operative connection in the electron relay 8 is represented by the characteristic curve 21 in Fig. 2.

Let it be assumed that normally the plate current is at a on the said curve 21 and that with an in-coming signal it will be reduced to the point (Z on the said curve, such action taking place when the stoppage condenser 6 is in series with the grid 16 and the accumulation of the various high frequency oscillations is such as to produce a negative charge on the grid 16 which reduces the plate current in a well known manner to a great extent.

When, however, the said variable resistance or by-pass functions so as to short circuit the stoppage condenser 6 and practically to eliminate the storing effect thereof, then the potential rises on the grid 7 of the electron relay 8 as is best indicated by the diagrammatic representation 34 in Fig. 4.

In such case, the functioning is on the curve 21 in Fig. 2 from the point 72 to the point 0 (symmetrically about the thus producing rapid diminution and rapid increases of the plate current, keeping exact step with the variations of the potential produced on the grid 7 by the individual high frequency oscillations acting thereon.

Thus there will be in the plate circuit symn'z trical fluctuations whose frequency is al to that of the high frequency oscillais of the transmitting station. If now the frequency of the oscillations of the transmitting station were equal to, say, one million per second, then the oscillating circuit containing the inductance coil 28 and the cond i 27. would constitute an impedance to it unidirectional high frequency 1mpr see which would be enormous. There fore the circuit containing the inductance. co l and the co .denser .27 would remain tota ly unalfected by such impulses, and would not transmit energy to the oscillatory circuit containing the inductance coil 29 and the condenser 30.

Thus, in a selective system which depends upon the use of a high frequency wave emitted at a specific group frequency, and having a receiving station operating through the joint action of the high frequency and its group frequency, the interference prerentor herein disclosed produces a still fun all) ther degree of selectivity, inasmuch as it modifies the functioning or operation of the electron relay 8 and changes its action so that whereas previously it allows unidirectional impulses of twenty thousand per sec- 0nd to traverse it, it now allows uni-directional impulses of a million to traverse it.

The stoppage condenser 6 is alternately thrown in and out of action by the functioning of the variable resistance or by-pass and when it is thrown into action it allows an accumulation of the high frequency oscillalions to take place, so that the true group effect, as illustrated at 33 in Fig. 4, passes through the electron detector or relay 8 in the unidirectional pulsations of direct current. hen the said condenser 6 is cut out, then no accumulation takes place in the grid 7 in the said electron relay, and the individual high freque cy pulsations of current are passed through the said electron relay 8, which, being entirely out of tune to the low frequency twenty thousand period cir- -cuit, cannot create in it oscillations to build up its resonance.

When employing an audion detector in the old way with the stoppage condenser on the grid, that adjustment of the grid potential which gives the greatest response in the plate circuit to the incoming groups of high frequency waves is the very adjustment which, when the stoppage condenser is short circui ted, will give absolutely no response in the plate circuit to the groups. My invention takes advantage of the said phenomenon and furnishes a leak for the stoppage condenser which does not become effective until voltage in excess of those encountered with the normal working signals are met with. l-zleavy static shocks and forced interference are allowed to get by this first audion with only little greater vigor than the normal workii'ig signals. In the case of randomly recurring shocks, such as those due to atmose pheric static electricity, this is suflicient to render them inappreciable in a subsequent tuned circuit.

In Figs. 5 and 6 respectively, I have diagrammatically indicated wing current fluctuations when the stoppage condenser is functioning normally and when said condenser is ell'ectively short circuited.

In Fig. 7, I have shown curves characteristic of the use of my invention.

Having thus described one embodiment of my invention and the mode best known to me for practicing the same, I desire it to be understood that although specific terms are employed, they are used; in a. generic or descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims.

1. A receiving system for radiant energy comprising in combination with a closed oscillatory circuit responsive to electrical oscillations, a three element thermionic detector opcratively connected tierewith, of a grid condenser connected in series between said closed oscillatory circuitand said de- 2' ctor, a thermionic valve in shunt with said id condenser aid means for varying the liuutt-ioning voltage of said shunt.

A receivin system for electrical imp1 ees coinpri a detector of electrical impulses includ rig a container, and ionizing means, pot ntial gradient changing means, and a terminal arranged in said container, a circuit responsive to electrical impulses and connected to said potential gradient changing means for controlling said detector, and a by-pass shunted around a portion of said circuit for protecting said detector from excessive impulses, said by including a container, and ionizing *ns, potential gradient changing means, pl a terminal arranged in said last-men- ,d container, a source of electric energy i..; heating said ionizing means, and a potentiometer in series with said source and adjustable to vary the functioning voltage of said by-pass.

3. A system for receiving electrical im-- pulses ci'iinprising a thermionic valve including a container, and ionizing means, potential gradient changing means, and a terminal enclosed in said container, a circuit responsive to electrical impulses and connected to said potential gradient changing means for controlling said thermionic valve. and a by-pass shuntec around a portion of said circuit for protecting said thern'iionic valve from excessive impulses, said by-pass including a container, and ionizing means, potential gradient changing means, and a terminal arranged in said last mentioned mutainer, a source of electric energy for heating said ionizing means and a potentiometer in series with said source and ad justable to vary the functioning voltage of said by-pass.

4:. A receiving system for radiant energy comprising a detector, a closed, oscillatory circuit responsive to electrical oscillations and operatively connected with the input side of the detector, an impedance element connected in series between the oscillatory circuit and the detector and across which high potentials may be induced, a device connected in shunt with said element and having a resistance which is much less for differences of potential above predetermined value than for smaller differences of potential, and means for varying the functioning voltage of said device.

5. A receiving system for radiant energy comprising a detector, a closed, oscillatory circuit responsive to electrical oscillations and operatively connected with the input side of the detector, a condenser connected in series between the closed oscillatory circuit and the detector, a device permanently connected in shunt to said condenser and having by reason of its construction and without continuing external control a resistance which is much less for differences of potential above a predetermined value than for smaller differences of potential, and means for varying the value of the difference in potential at which said device functions to short-circuit the condenser.

6. A receiving system for radiant energy comprising a three-electrode thermionic detector, a closed, oscillator circuit responsive to electrical oscillations and operatively con nected with the input side of the detector, an impedance element connected in series between the oscillatory circuit and the grid of the detector and across which high potentials may be induced. a thermionic tube connected in shunt with said impedance ele ment and acting to oppose less resistance to the passage of currents at high potentials than at low potentials, and means for varying the functioning voltage of said tube.

7. A receiving system for radiant energy comprising a detector, a closed, oscillatory circuit responsive to electrical oscillations and operatively connected with the input side of the detector, an impedance element connected in series between the oscillatory circuit and the detector and across which high potentials may be induced, a three electrode thermionic tube connected in shunt with said impedance device and acting to oppose less resistance to the passage of currents at high potentials than at low potentials, means for impressing a constant positive potential on the grid of said tube as compared with the filament, and a variable resistance connected in series between the tube and said impedance device for varying the functioning voltage of the tube.

8. A receiving system for radiant energy comprising an impedance element across the terminals of which high potentials may be induced, and a b v-pass for said element including a three-electrode thermionic tube having its plate and filament connected across the terminals of the element, a source of potential between the grid and filament of said tube, and means for varying the functioning voltage of the tube comprising a potentiometer connected in parallel with the filament and a connection between the potentiometer and one of the terminals of the element.

9. A receiving system for radiant energy comprising a detector, a source of energy on the input side of the detector, an impedance element connected in series between said source of energy and the detector and across which high potentials may be induced, a de vice connected in shunt with said element and having inherently and without continu external control a resistance which is much less for ditlerences of potential above a predetermined value than for smaller dif ices of potential, and means for varying e functioning voltage of the device.

i A receiving system for radiant energy comprising a detector, a Source of energy on the input side of the detector in the form of a transformer having its secondary winding connected with the detector, an impedance element connected in series between said winding and the detector and across which high potentials may be induced, a device connected in shunt with said element and having inherently and without continuing external control a resistance which is much less for dite "ences of potential above a pre determined value than for smaller differ ences of potential, and means for varying the functioning voltage of the device.

11. A receiving system for radiant energy comprising a three-electrode thermionic detector, a closed, oscillatory circuit responsive to electrical oscillations and operatively con nected with the input side of the detector, an impedance element connected in series between the oscillatory circuit and the grid of the detector and across which high potentials may be induced, a device permanent ly connected in shunt with said element and having a resistance which in direct response to potentials impressed across its terminals is much less for differences of potential above a predetermined value than for small er differences of potential, and means for varying the functioning voltage of the device.

12. A system for receiving radiant energy in the form of a series of high frequency waves modulated at a regular periodic group frequency above good audibility, comprising a detector, a closed, oscillatory circuit arranged. on the input side of the detector and tuned to said high frequency, a closed oscillatory circuit connected with the output side of the detector and tuned to the group frequency, an impedance element connected with the input side of the detector and a device permanently connected in shunt with said impedance element for short-circuiting it for potentials above a predetermined value.

In testimony whereof, I have signed my name to this specification.

JGHN HAYS HAMMOND, JR.

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